The invention relates to a method of manufacturing a permanent magnet which comprises a hard magnetic material having a tetragonal phase of the RE.sub.2 Fe.sub.14 B type, wherein RE is at least one element selected from the group consisting of the rare earth metals having atomic number 57 up to and including 71 and Yttrium, the method comprising the following steps
1. forming an alloy comprising 8-30 at. % RE, 2-28 at. % B and 42-90 at. % Fe PA1 2. pulverizing the alloy into a powder PA1 3. compressing the powder, whether or not in a magnetic field, into a shaped body PA1 4. sintering the shaped body in the temperature range from 900.degree.-1200.degree. C., after which the body may be magnetized.
Such a method is known from European Patent Application No. 153.744. In the method described therein, a powder of an alloy of the above composition and having an average particle size from 0.3-80 .mu.m is compressed into a shaped body, after which this body is converted into an end-product by subjecting it to three heat treatments. These heat treatments successively comprise a sintering treatment (900.degree.-1200.degree. C., preferably for 0.5 to 4 hours), a first heat treatment (750.degree.-1000.degree. C., preferably for 0.5 to 8 hours) and a second heat treatment 480.degree.-700.degree. C., preferably for 0.5 to 12 hours). These heat treatments contribute to obtaining magnets having favourable hard magnetic properties such as a high density, a high remanence and a large energy product.
The well-known method has the disadvantage that the heat treatments take up a considerable amount of time. If mass production in a continuous process is pursued, the duration of the heat treatments is an insuperable problem from an economic point of view. In such a continuous process, magnets are individually formed by successively compressing a powder, sintering the shaped body obtained and inspecting it for mechanical and magnetic properties.